Chondrocytes are cells which originate from chondroblasts and are located in cartilage tissue. In fully grown cartilage, chondrocytes lie together in isogenic groups (up to about 10) surrounded by extracellular substance. They make up less than 10% of the bone volume. Owing to their high synthesis activity, they have many organelles and large Golgi complexes. In healthy cartilage, chondrocytes have a low mitosis rate. They synthesize specific matrix components and accumulate them as hyaline cartilage substance, and change their synthesis rate with altered loading pattern.
Hyaline cartilage is found wherever mainly pressure loads occur, which is why it is mostly found in articular cartilage. Nowadays, cartilage defects and degenerative joint diseases are among the most widespread diseases. A distinction is usually made between diseases of the cartilage in which the destruction of articular surfaces can probably be traced back mainly to load impacts, and diseases in which articular degeneration owing to inflammation is at the forefront.
Apart from the (in part very) painful accompanying symptoms of these diseases, they are also a major issue in healthcare since the treatment of joint defects is very cost-intensive which, not least, can also be attributed to the high number of disease cases.
Since the capacity of hyaline cartilage for endogenous regeneration is restricted by nature, a surgical procedure for treating cartilage defects is usually the only alternative for a therapy which is successful to at least some extent. Common to the therapy approaches currently used is the goal of restoring cartilage mass, of a congruent articular surface, of physiological functionality and freedom from pain. Recently, autologous chondrocyte transplantation/implantation (ACT or ACI) in particular has emerged as a preferred measure. In the context of ACT, a cartilage biopsy from a healthy area far from the main articular load zone is removed in a first surgical procedure. From the matrix network of the biopsy, chondrocytes are liberated enzymatically, isolated, and expanded in vitro. After about two weeks and successful cell expansion, the joint is reopened and cleared of debris. Subsequently, a periostal patch (periosteum) from the patient is sutured over the defect, creating a chamber filled with the chondrocyte suspension.
ACT has, however, some disadvantages which have meanwhile been confronted by, in particular, the implantation of cells/chondrocytes applied to biomaterials.
For example, a bioresorbable, biphasic collagen support (NOVOCART® 3D, TETEC AG, Reutlingen, Germany), colonized by autologous chondrocytes, is transplanted into cartilage-bone or pure cartilage defects. While the cells mediate biological restoration of the defective cartilage, the biphasic support facilitates intraoperative handling and provides, in vivo, mechanical protection of the implanted cells and of the newly developing cartilage tissue. Furthermore, the support also ensures that the chondrocytes to be implanted remain at the site of the defect, this being very often quite a big problem in the case of conventional ACT, i.e., ACT with a periostal patch cover.
Nevertheless, the selection, identification and culturing of chondrocytes, both in conventional ACT and in use of support-assisted ACT, or of chondrocyte implantations in general, is a major challenge. This is because chondrocytes can vary greatly with respect to their suitability for use as autologous cells for implantation for cartilage regeneration. This is true not only for chondrocytes from one donor in relation to chondrocytes from another donor, for example, a healthy donor compared to a sick donor, but also for chondrocytes from the same donor. In addition, chondrocytes can change in their properties in an ex vivo culture such that they are no longer as suitable for implantation as when accepted directly after isolation from the donor.
Therefore, it would be desirable to develop a method by which chondrocytes can be checked for their suitability for a prospectively successful chondrocyte transplantation, for example, to have criteria which are indicative thereof.